1. Field of the Invention
The present invention relates generally to a control system for controlling delivery of driving torque for an automotive vehicle. More specifically, the invention relates to a control system for the magnitude of driving torque to be delivered to driven wheels for optimizing vehicular driving performance. Further particularly, the invention relates to a control system for controlling driving torque primarily depending upon a torque demand to be delivered to driven wheels.
2. Description of the Background Art
Japanese Patent First (unexamined) Publication (Tokkai) Showa 60-192843 discloses a control system for adjusting driving torque generated in response to operation of an accelerator pedal. The disclosed system adjusts a throttle valve open angle toward a set angle on the basis of the operational magnitude of the accelerator and an engine revolution speed. On the other hand, Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 62-193151 discloses a similar control for a Diesel engine, in which a governer is controlled instead of the throttle valve. Furthermore, Japanese Patent First Publication (Tokkai) Showa 63-25355 discloses adjustment of the engine output depending upon the vehicle driving condition so as to establish desired driving performance.
In the foregoing or other prior proposed engine control systems, the engine output torque is controlled toward a target torque set according to an operational magnitude of an accelerator pedal. In the practice, the target torque set in relation to the operational magnitude of the accelerator pedal is adjusted in view of possible maximum torque (hereafter referred to as "critical torque") depending upon road/tire slippage in feedback manner. When the control system is established for performing engine output control based on the engine output torque to be generated corresponding to the operational magnitude of the accelerator pedal, however the driving torque to be delivered to the driven wheel tends to become excessive, particularly on a relatively low friction road. Therefore, it becomes necessary to provide a separate traction control system.
In general, the automative internal combustion engine is connected to the driven wheels via a power train including an automatic power transmission or automatic transaxle incorporating a torque converter. In such case, the driving torque to be delivered to the driven wheel cannot be precisely controlled solely by controlling the engine output torque because of slippage at the torque converter. Furthermore, response characteristics of driving torque delivery are determined depending not only upon the engine characteristics but also upon responsive characteristics of the automatic power transmission or the automatic transaxle.